EPIC Upper Limits - XMM-Newton
XMM-Newton Upper Limits
Upper limits, from the three EPIC cameras, have been pre-calculated and stored in a database for slew and pointed observations which are public. This is an on-going process with new observations being added as they become available. They have been calculated at 1,2 and 3-sigma significance using 1-sided Bayesian statistics, which correspond to confidence probabilities of 84.13, 97.72 and 99.87% that the true count-rate value lies below the respective upper limit.
Values are available for soft (0.2-2 keV), hard (2-12 keV) and total (0.2-12 keV) energy bands.
Conversion from count-rate to flux is dependent on the camera, on the filter used in the observation and on the assumed spectrum. Factors are given in the following table, in units of [1E11 cts cm^2/erg], for a spectrum of a power-law of slope 1.7 absorbed by a column, NH=3E20 cm^2.
The same conversion factors are used to calculate source fluxes in the 4XMM source catalogue:
|Instrument||Filter||Energy Conversion Factor (ECF)|
|0.2 - 2.0 keV||2.0 - 12.0 keV||0.2 - 12.0 keV|
Flux = count-rate / ECF (erg/cm^2/s)
Upper limit records are shown when the input position lies within the field-of-view of a pointed or slew observation and is not close to a detected source, is not close to a chip gap or the edge of the field and where, for pointed observations, the background is non-zero.
Upper limits are calculated from pipeline images using aperture photometry. Source counts are extracted from a circle of radius of 15 arcseconds (pointed) and 30 arcseconds (slew). Background counts for pointed data are extracted from background maps, with a circle of radius 60 arcseconds. For slew observations, background counts are extracted from an annulus of inner radius 60 arcseconds and outer radius 120 arcseconds.